The present invention relates to a metal gasket, which is clamped between two joining surfaces and seals the joining surfaces with a bead thereof, the metal gasket including the bead surrounding at least one hole for fluid, which allows openings for fluid to be communicated with each other, the openings being provided in the respective joining surfaces.
As a metal gasket mentioned above, for example as shown in FIG. 7, a metal gasket 3 which is held between two joining surfaces 1 and 2, which are joining surfaces with an engine cylinder head and with an EGR plate which is installed on an intake manifold and on which a gas passage concavity for EGR system is formed, is included. Such a metal gasket 3 usually has an intake through hole 3a connecting an intake port 1a and an intake pipe port 2a, which are provided, as openings for fluid, each on the joining surface 1 of the cylinder head and the joining surface 2 of EGR plate installed on the intake manifold, and a full bead 3b having a cross section of a chevron shape as a bead surrounding the intake through hole 3a (It looks V shape in the drawing). Whole circumference of the full bead 3b is interposed between the joining surfaces 1 and 2, which are urged in the closing direction each other by fitting bolts (not shown in the drawing) as shown by an arrow A in the drawing, and is pressed strongly by the joining surfaces 1 and 2. Thus, high surface pressure is generated on whole circumference of the full bead 3b to exert high sealing properties.
At the request for further engine exhaust gas cleaning and more improvement in fuel consumption and the like in recent years, there have been a possibility that as shown in FIG. 8, the foregoing gas passage concavity 2b, lightning holes and lightning hollows for weight reduction (not shown in the drawing) are formed in an opposite position to a part of bead 3b on a joining surface 2 of an EGR plate installed on the an intake manifold, which is one of two joining surfaces 1 and 2 holding a metal gasket 3 therebetween. When portions without pressuring surface such as the gas passage concavity 2b, the lightning holes and the like are formed, in a single plate-type metal gasket 3 which has been used conventionally, the portions of bead 3b opposite to the portions without pressuring surface such as the foregoing gas passage concavity 2b, the lightning holes and the like should be originally pressurized to the other joining surface as shown with a dashed lined in the drawing. However, there is no surface to push the portions of bead 3b, and the areas of bead 3b can be escaped to an area without pressuring surface as shown with a solid line in the drawing. Therefore, there has been a problem that the areas of bead 3b are not pressurized strongly enough to the joining surface 1 of cylinder head which is the other joining surface and sealing properties in the areas of bead 3b decrease. It has been particularly a problem that the decrease of the sealing properties is especially remarkable when the metal gasket 3 is held between the foregoing joining surface 1 of a cylinder head and the joining surface 2 of EGR plate where pressure in the openings becomes negative pressure since the openings for fluid are an intake port 1a and an intake pipe port 2a. 
Then, in order to secure sealing properties on whole circumference of the bead, a laminated metal gasket was studied, in which a gasket constitutional plate being adjacent to the other joining surface mentioned above, has a bead. The areas of the bead opposite to portions having no pressuring surface such as a gas passage concavity and a lightning hole and the like on one joining surface mentioned above, are pressurized by other gasket constitutional plate to the other joining surface. In this way, however, there has been a problem that sometimes the above described method could not satisfy the request for weight reduction and cost reduction sufficiently since weight of a metal gasket as a whole is increased and also manufacturing cost is increased.